1997 年 46 巻 2 号 p. 103-112
Chloride stress corrosion cracking (SCC) has been a problem for austenitic stainless steel in aqueous environments containing chlorides. Studies have found that SCC initiates only from a dissolving surface and under the condition that the crack growth rate is higher than the dissolution rate of the dissolving surface. Research conducted to improve the resistance to SCC for Type 304 steels (UNS S30400) has revealed that while molybdenum and phosphorus are unfavored, the alloying of 3% aluminum combined with 2% copper can almost nullify their detrimental effect. Based on the mentioned criteria, this study was dedicated to clarify the mechanism behind these alloying effects by examining the relationship between the measured enhancements on SCC resistance and the dissolution rate observed by the moire technique. It was found that the addition of both molybdenum and phosphorus reduces the dissolution rate and therefore impaired SCC resistance; the addition of copper increases the dissolution rate of the steady growth stage where crevice corrosion proceeds at a constant rate. Moreover this dissolution rate could further be increased when combined with the alloying of aluminum. These observed results correspond well to that of the measured behavior of the SCC critical temperature, Tc, suggesting that the SCC susceptibility is influenced by anodic dissolution.
